Maghemite nanoparticles protectively coated with poly(ethylene imine) and poly(ethylene oxide)-block-poly(glutamic acid)

Superparamagnetic iron oxide particles (SPIO) of maghemite were prepared in aqueous solution and subsequently stabilized with polymers in two layer-by-layer deposition steps. The first layer around the maghemite core is formed by poly(ethylene imine) (PEI), and the second one is formed by poly(ethylene oxide)-block-poly(glutamic acid) (PEO-PGA). The hydrodynamic diameter of the particles increases stepwise from D(h) = 25 nm (parent) via 35 nm (PEI) to 46 nm (PEI plus PEO-PGA) due to stabilization. This is accompanied by a switching of their zeta-potentials from moderately positive (+28 mV) to highly positive (+50 mV) and finally slightly negative (-3 mV). By contrast, the polydispersity indexes of the particles remain constant (ca. 0.15). M?ssbauer spectroscopy revealed that the iron oxide, which forms the core of the particles, is only present as Fe(III) in the form of superparamagnetic maghemite nanocrystals. The magnetic domains and the maghemite crystallites were found to be identical with a size of 12.0 +/- 0.5 nm. The coated maghemite nanoparticles were tested to be stable in water and in physiological salt solution for longer than 6 months. In contrast to novel methods for magnetic nanoparticle production, where organic solvents are necessary, the procedure proposed here can dispense with organic solvents. Magnetic resonance imaging (MRI) experiments on living rats indicate that the nanoparticles are useful as an MRI contrast agent.     

Spin-lattice interaction in the quasi-one-dimensional helimagnet LiCu2O2

The field dependence of the electron spin resonance in a helimagnet LiCu2O2 was investigated for the first time. In the paramagnetic state, a broad resonance line was observed corresponding to a g factor of 2.3. In the critical regime, around the paramagnetic to helimagnetic phase transition the resonance broadens and shifts to higher frequencies. A narrow signal is recovered at a low temperature, corresponding to a spin gap of 1.4 meV in zero field. A comprehensive model of the magnons is presented, using exchange parameters from neutron scattering [T. Masuda Phys. Rev. B 72, 014405 (2005)10.1103/PhysRevB.72.014405] and the spin anisotropy determined here. The role of the quantum fluctuations is discussed.     

The plane grating and elliptical mirror: A new optical configuration for monochromators

A new optimal focussing kinematically simple two-element optics for plane grating monochromators is described. It will be used to monochromatise synchrotron radiation in the soft X-ray region.     

Elektronenoptische Untersuchung des magnetischen Streufeldes über (110)-Flächen prismatischer Nickel-Einkristalle

An experiment is described that realizes a suggestion for measuring the magnetic stray field above the surface planes of ferromagnetic single crystals with defined shape and orientation. The cause of the deflection of the electrons in the resulting electron optical shadow-image is investigated and the problem is discussed, wether the deflections are due to “magnetic charges” of planes or lines. The experiments undertaken so far favour magnetic lines, i.e. the intersections of the Bloch-walls with the crystal surface, and make a quantitative evaluation of their leakage field possible. Calculations from our experimental data give a tangential field of about 3 Oe immediately at the surface between two Bloch-walls, and assuming line charges a normal field of about 100 Oe at a distance of 1μ above a 71°-Bloch-wall.     

Quantitative r?ntgenspektralanalytische Bestimmung von Kalium, Rubidium, Strontium, Barium, Titan, Zirkonium und Phosphor

Zusammenfassung Am Malsburg-Granit, einem geologisch selbständigen Granitpluton im Südwest-Schwarzwald, wurde die lokale Heterogenität der Elemente Kalium, Rubidium, Titan, Zirkonium, Phosphor, Strontium und Barium mit Hilfe der Röntgenspektralanalyse bestimmt, um anschließend die Heterogenität des gesamten Gesteinskörpers zu erfassen.Die Analysenergebnisse sind reproduzierbar, wenn das Gesteinsmaterial nach systematischer Probenahme auf eine Korngröße <37 aufgemahlen wird. Es wurden die Fehler bestimmt, die durch Zählstatistik, das Meßverfahren und die Aufbereitung entstehen. Dabei ergab sich, daß die gefundenen Fehler für 95% Sicherheit stets kleiner sind als die Streuung der Elemente in einem Steinbruch bzw. im gesamten Granitkörper.

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Summary The local heterogeneity of K, Rb, Ti, Zr, P, Sr and Ba was determined by X-Ray Fluorescence Analysis as a first step in our investigations concerning the determination of the regional heterogeneity of a whole granite body of larger extent. The first granite of this series is the Malsburg-Granite in the South-West of the Black Forest.The analytical results are reproducible and accurate, if the rock samples are ground below 450 mesh. The errors and mean deviations caused by counting, instrumentation and preparation are small in comparison with those in a rock sample of an outcrop or the whole rock body.The method of X-Ray Fluorescence Analysis can be applied for the study of the mechanism of magmatic intrusion and differentiation.

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Auszug aus Dipl.-Arbeit H. Ackermann, 1962, Frankfurt/M, unveröffentlicht.

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Wir danken der Deutschen Forschungsgemeinschaft für apparative und finanzielle Hilfe.     

Effects of surface hydrophobization on the growth of self-assembled monolayers on silicon

The growth of self-assembled monolayers from octadecyltrichlorosilane (OTS) on modified silicon surfaces has been investigated. The influence of different immersion times in a deactivation reagent on the growth mechanism and the ordering of the films has been studied. Characterization of the films and the submonolayer coverage has been performed with tapping mode atomic force microscopy, ellipsometry, and infrared spectroscopy. We found that a deactivation of active sites led to a higher mobility of adsorbed molecules on the surface resulting in circular islands of highly ordered alkylsiloxane. However, upon prolonged immersion in OTS these ordered islands did not continue to grow and full monolayer coverage could not be obtained. Instead, an exchange reaction with the deactivation reagent leading to a disordered film between the ordered islands was observed. This was confirmed by external reflection infrared spectroscopy.     

One-dimensional instability in BaVS3

The 3d(1) system BaVS3 undergoes a series of remarkable electronic phase transitions. We show that the metal-insulator transition at T(MI)=70 K is associated with a structural transition announced by a huge regime of one-dimensional (1D) lattice fluctuations, detected up to 170 K. These 1D fluctuations correspond to a 2k(F)=c(*)/2 charge-density wave (CDW) instability of the d(z(2)) electron gas. We discuss the formation below T(MI) of an unconventional CDW state involving the condensation of the other V4+ 3d(1) electrons of the quasidegenerate e(t(2g)) orbitals. This study stresses the role of the orbital degrees of freedom in the physics of BaVS3 and reveals the inadequacy of current first principle band calculations to describe its electronic ground state.